Claudia-Elisabeth Wulz
Institute for High Energy Physics
Vienna
CMS Week
Mumbai, Dec. 2000

Definition of Trigger Menu:
Set of algorithms running concurrently in the Global Trigger.
There may be different sets for different run conditions (Bphysics at low luminosity, heavy ion runs, discovery physics at high luminosity, calibration etc.). Run control must record the used menu.
Remember: If an event does not pass Level-1, it is gone forever
Claudia-Elisabeth Wulz 2 Mumbai, Dec. 2000

Trigger
1 µ
2 µ
µ +e/ γ
µ +jet(s)
µ +E
T m
1 e/ γ
2 e/ γ
2 jets e/ γ +jet(s)
µ + τ e/ γ + τ
τ +jets jets+E
T m
Claudia-Elisabeth Wulz
Examples of explorable physics channels
H
SM
, H, A, H ± , W, W’, t, B-physics channels
H
H
SM
SM
H
SM
, h, H, A, Z, Z’, V, , LQ, B
, H, A, t, WW, WZ, W
, h, H, A, , LQ, t
γ , , V t, , LQ, WW, WZ, W γ l , ˜ 0 , ˜
± s
0 ->2 µ , ϒ , ϒ ’, ϒ ’’
H
SM
H
SM
H
SM
H
SM
H
H ±
SM
, h, H, A, W, W’, t, B-physics channels
, h, H, A, Z, Z’, WW, WZ, W
QCD
γ χ ±
, h, H, A, , LQ, QCD ( γ +jets, W+jets)
, H, A,
, H, A,
, H ±
3 Mumbai, Dec. 2000

Established during TriDas Week 9 Nov. 2000. Every interested person is invited to join and to provide his or her ideas !
!
Presentations at initial meeting:
• Introduction
• Global Trigger overview
• Calorimeter Trigger overview
• Muon Trigger overview
• Trigger menu requirements from physics point of view
• Trigger menu requirements from HLT point of view
• Trigger menu requirements from DAQ point of view
Claudia-Elisabeth Wulz 4
W. Smith
C.-E. Wulz
S. Dasu
G. Wrochna
M. Dittmar
P. Sphicas
S. Cittolin
Mumbai, Dec. 2000

l
Provide initial trigger menus to capture the interesting physics.
Menus for calibration etc. should also be established. Menus should not be considered fixed once and for all, but will evolve with experience gained. The flexibility and special features of the
CMS L1 trigger should be optimally used.
l
Check that trigger design is capable of handling all physics and technical requirements.
l
Provide corresponding suitable trigger parameters (at level of global trigger and at regional and perhaps local levels).
l
Allocate suitable bandwidths for categories of algorithms.
Claudia-Elisabeth Wulz 5 Mumbai, Dec. 2000

Claudia-Elisabeth Wulz
GLOBAL TRIGGER
Global Calorimeter
Trigger
Regional Calorimeter
Trigger
Regional DT
Trigger
Global Muon Trigger
Regional CSC
Trigger
Calorimeter
Local Trigger
Calorimeter energy
DT
Local Trigger
DT
Hits
CSC
Local Trigger
CSC
Hits
RPC
Trigger
RPC
Hits
6 Mumbai, Dec. 2000

For most other comparable experiments the trigger is based on counting objects exceeding thresholds. Only summary information is available. This implies applying thresholds at local or regional levels. In CMS, only the Global Trigger takes decisions, i.e. no cuts (except inherent thresholds for defining a jet, isolation criteria etc.) are applied by lower level trigger systems. The trigger decision is based on detailed information about a trigger object, which includes not only p
T
or E
T
, but also location. For muons, quality information and charge are also available. This enables selecting specific event topologies. The objects are ordered by rank.
An algorithm is a combination of trigger objects satisfying defined threshold, topology and quality conditions.
There are 128 trigger algorithms running in parallel. The resulting bits are available in the trigger data record. The Global
Trigger runs dead-time free by principle, i.e. a L1 Accept/Reject decision is issued with every bunch crossing. The Trigger Throttle System may, however, inhibit a
L1A in case of e.g. buffer overflow warning. For each algorithm a rate counter and a programmable prescale factor (up to 16 bits) are available.
The L1 decision is taken by a Final OR of which up to 8 are available for physics.
Claudia-Elisabeth Wulz 7 Mumbai, Dec. 2000

For physics running the Global Trigger uses only input from the calorimeters and the muon system.
Trigger specific sub-detector data are used. The high resolution data are used by the Higher Level
Triggers. Apart from the trigger data, special signals from all sub-systems may be used for calibration, synchronization and testing purposes (technical triggers).
The TTC System is an optical distribution tree that is used for the transfer of the Level-1 Accept signal and timing information (LHC clock etc.) between the trigger and the detector front-ends.
The Trigger Control System controls the delivery of L1A signals and issues bunch crossing zero and bunch counter reset commands. There is a facility to throttle the trigger rate in case of buffers approaching overflow conditions.
The Event Manager controls the Higher Level Triggers and the Data Acquisition.
L1 calorimeter trigger
L1 muon trigger
Technical triggers
GLOBAL
TRIGGER
PROCESSOR
Trigger
Control
System
TTC system
DAQ
Event
Manager
Detector
Front-Ends
Global Trigger Environment
Claudia-Elisabeth Wulz 8 Mumbai, Dec. 2000

Best 4 isolated electrons/photons
Best 4 non-isolated electrons/photons
Best 4 central jets (| |
3
)
Best 4 forward jets (3 | |
5
)
Best 4 - jets
Total E
T
Missing E
T
6 jet counts (central jets)
2 jet counts (forward jets)
Best 4 muons
E
T
, ,
E
T
, ,
E
T
, ,
E
T
, ,
E
T
, ,
Σ
E
T
E
T miss , (E
T miss ) p
T
, sign, , , quality, MIP, ISO
4 inputs (approximately 100 bits) are still free.
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 9

The Global Trigger logic is largely programmable.
Particle energy or momentum thresholds and (or windows can be set separately for each object. Different thresholds for central and forward regions are therefore possible.
Templates for muon quality , including MIP, isolation and charge information can be selected.
Space correlations are possible between all objects, but restricted to “close” and “opposite/far”.
Jets are actually separated into central and forward jets. There are also 8 jet multiplicities , 2 of which are reserved for the forward jets.
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 10

In the stable phase of the experiment the trigger is set up via
Run Control using predefined menus which include reasonable thresholds for different luminosities. These thresholds may be changed by the physicist, without reconfiguring the logic chips.
Most of the 128 algorithms are available for physics running.
The basic rule is to keep the trigger menus as simple as possible.
If not all interesting physics processes can be caught with these, more sophisticated logic may be used, but careful studies of trigger efficiencies have to be made.
If a new algorithm (i.e. one not already present on the chips) becomes necessary, the chips can be reprogrammed by experts.
The timescale for this is a few hours, but it should not happen too often.
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 11

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Claudia-Elisabeth Wulz 15 Mumbai, Dec. 2000

Trigger Primitives
Fine grain veto: max E
Trigger Towers
Separate E
H/E veto:
T
in -strip pair vs total trigger tower E
T
T
cutoffs for e/ and /jet/E
ECAL vs HCAL E
T
T
triggers
ratio, can be non-linear
Active tower definition: programmable E
T pileup
cut to adjust for
4x4 trigger tower region level for jets: E
T
cut for pileup suppression, cut on active tower count for veto
/jet candidate level: -dependent center region threshold and
E
T
lookup
Possible additional Global Calorimeter Trigger algorithms:
E
T
of jets, missing E
T
of jets
Claudia-Elisabeth Wulz 16 Mumbai, Dec. 2000

p
T
scale of all 3 systems (DT, CSC, RPC) programmable, can in principle be different for all 3, but Global Muon Trigger must convert to a common scale.
Implementation of the matching scheme, many tunable parameters
TRACO: LUTS for correlation of BTIs, filters for ghost suppression
Track Finder: Extrapolation windows, assignment LUTs, filters for ghosts (also in Global Muon Sorter) patterns, gate (noise suppression)
Claudia-Elisabeth Wulz 17 Mumbai, Dec. 2000

Disentangle detector and trigger malfunctions, monitor rejected events
Regional reconstruction of HLT depends on what L1 sends!
Need to reconstruct also objects that did not fire the L1 trigger.
Need database, pointer to it is major element of “run number”.
Event is not simply identified by run and event number, but by data structure containing run conditions. Run = time between fill start and end.
Need full reconstruction. Example of use: check events that systematically fail e/ trigger, but fire the jet trigger.
Claudia-Elisabeth Wulz 18 Mumbai, Dec. 2000

Automatic or fixed. For automatic prescaling need good and traceable luminosity measurement! Check trigger efficiencies at lower thresholds than in main trigger menu, flag events for calibration.
Relax thresholds and optionally change algorithms as luminosity drops.
Option in the Global Trigger, no strong demand yet ...
Should be in database accessible both by the Global Trigger Processor and the HLT farm.
Local event filter rate 1000 Gbit/s, event storage 5 Gbit/s. Recording rate can be greater than 100 Hz.
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 19

Hardware Trigger(< 100 kHz) raw calibration subdetectors with coarse detector segmentation single (isolated) objects with p
T
cuts multiple object triggers
η φ correlations satisfy physics needs with hardware
HLT (< 100 Hz) almost final calibration almost full detector fine segmentation and
combination of tracks calo and µ system verify trigger object(s) object matching with tracks mass of clusters + tracks satisfy physics requirements with software
Analysis (10 6-7 events?) best calibration full detector available signal optimization accurate track matching precision mass calculations
complicated η , φ and p
T
selection criteria be "undisturbed" by trigger conditions
Trigger cuts should be softer than physics selection criteria, but some rates will be too high! Need compromise.
High Q 2 : Exciting, possibly exotic physics
Medium Q 2 and low x physics: New domain of strong interactions
Low Q 2 : b and c physics with unprecedented statistics
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 20

Physicists have many different points of view.
Examples:
Rapidity gap events are interesting/boring
Can(not) trigger on invisible particles (e.g.
Physicists want redundancy.
Example: high mass Drell-Yan lepton pairs
X events)
After discovery physicists want to explore.
Need to study more difficult signatures.
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 21

10 7 events/day at rate of 100 Hz
Accuracy for cross-section measurements: ± 1%
-> 10 5 accepted signal events -> ± 0.3% statistical error
Cross section ( x BR) Events/day Comment
1 mb
1
µ b
100 nb
10 nb
1 nb
10 11
10 8
10 7
10 6
10 5
Can redo every hour
Can redo daily
Do in early running
Do in early running
Do in early running
1 pb
1 fb
100
0.1
If not triggered …
gone forever!
Claudia-Elisabeth Wulz 22 Mumbai, Dec. 2000

•
•
Low cross section
Important not to lose any event
Example: B s o -> + (BR ≅ 3.5 x 10 -9 )
After discovery can accept worse S/B ratio for
BR measurements
•
•
•
•
Large cross section ( x BR > 100 nb)
Prescaling
Accept 1 Hz rate for a few days and make analysis
Use luminosity lifetime: use free rate near end of fill
Combination of all three above
Claudia-Elisabeth Wulz Mumbai, Dec. 2000 23

•
•
•
•
Physics goals
Observation, evidence, exclusion
Cross section measurement
BR measurement
Measurement of trigger effiency
(control channels, lower thresholds, etc.), background
•
•
•
•
Simulation studies to be done
SM Higgs, SUSY, higher dimensions, exotica, … b and t physics
QCD and other SM physics
New signatures as we go along
Claudia-Elisabeth Wulz 24 Mumbai, Dec. 2000

Redundancy for high Q 2 processes
Rates for many single object triggers relatively high, multiobject triggers should be made use of
Need scenarios for use
Claudia-Elisabeth Wulz 25 Mumbai, Dec. 2000